1. Field of the Invention
This invention relates to ballistic resistant body armor.
2. Description of Related Art
Many designs for body armor for resisting ballistic threats have been proposed and many commercialized. Designs are made to increase comfort by the wearer to increase their use. Comfort is generally increased by making them lighter and more flexible to allow freedom of motion by the wearer. However, apparel weight needs to be increased to provide protection against projectiles with greater velocities and mass. It is also desirable to minimize the costs to make the apparel, but traditional materials used in body armor are relatively expensive.
Standards have been proposed and adopted throughout the world to ensure minimum capabilities of body armor for resisting ballistic objects. See NIJ Standard—0101.04 “Ballistic Resistance of Personal Body Armor”, issued in September 2000. It defines capabilities for body armor for level IIA, II, IIIA and III protection. To achieve level 11 protection, the armor must have no penetration and no more than a backface deformation of 44 mm by a projectile such as a 0.357 magnum projectile at a velocity (Vo) defined as 1430 ft/sec plus or minus (+/−) 30 feet per sec (436 m/sec +/−9 m/sec). To achieve level IIIA protection, the armor must have no penetration and no more than a backface deformation of 44 mm by a 0.44 magnum or similar projectile at a velocity (Vo) defined as 1430 ft/sec plus or minus (+/−) 30 feet per sec (436 m/sec +/−9 m/sec). Body armor is frequently designed with a margin of safety surpassing the requirements of the Standard. However, increasing the margin of safety typically increases the cost and weight and decreases the flexibility of the body armor. So body armor is typically made to meet published standards with a small margin of safety.
There are also many designs for body armor for resisting spike (e.g., ice pick like) or knife stabbing or slashing threats. However, such designs typically are not optimum or even necessarily able to protect against ballistic threats. Separate standards have been published providing different tests and requirements for such spike or knife resistant body armor compared to standards for ballistic resistant body armor. Thus, those skilled in the art do not assume teachings on making or optimizing spike or knife resistant body armor are useful in designing ballistic resistant body armor.
Body armor meeting the NIJ ballistic standard level 11 or IIIA protection can be made solely of woven fabric layers made from high tenacity multifilament yarns, such as made from para-aramid. Such woven fabric layers provide very good penetration resistance against bullets and fragments. However, woven fabric layers alone provide less protection against backface deformation requiring more layers and increased weight to meet the margin of safety or even the standard. Hybrid body armor meeting the level II or IIIA protection can be made using a plurality of such woven fabric layers stacked in combination with a plurality of unidirectional assemblies comprising a unidirectional tape made of an array of parallel high tenacity multifilament yarns in a matrix resin stacked with adjacent tapes with their yarns at angles inclined with respect to adjacent tapes. Typically the yarns in the tapes are at right angles with respect to yarns in adjacent tapes. These hybrid body armors provide good penetration resistance against bullets, greater protection against backface deformation, but replacing woven fabric layers with unidirectional assemblies reduces protection against fragments, increases rigidity and increases cost. Body armor meeting the level II or IIIA protection can be made solely using a plurality of the unidirectional assemblies. They provide good penetration resistance against bullets, very good protection against backface deformation, but they typically provide the least protection against fragments, are more rigid than the other options, and are the most expensive.
U.S. Pat. No. 6,030,683 to Chitrangad describes the positioning of a pulp layer between woven fabric layers to provide increased wearer comfort and flexibility. The pulp is made by refining short length fibers (floc) to fibrillate them thus yielding splayed ends and hair-like fibrils extending from the fiber trunk. The pulp is compressed into a paper having a thickness of between 0.5 to 5 millimeters. Assemblies comprising woven fabric layers and pulp sheets were evaluated against 22 caliber fragment simulating projectiles. Results showed up to 5% deterioration in ballistic resistance when compared with an equivalent weight assembly comprising only woven fabric. While considered acceptable for protection against fragments, such a pulp sheet assembly does not provide protection against deformable projectiles such as a 0.44 magnum bullets that have higher impact energies.
It is an object of this invention to provide improved body armor designs that utilize the advantages of woven fabric layers described above without incorporating unidirectional assemblies and their associated disadvantages.
These and other objects of the invention will be clear from the following description.